EMRFD Message Archive 13371

Message	Date	From	Subject
13371	2016-12-17 20:37:45	ad7zu	Grounding Rules?
I am working on an audio analog to digital converter board and even by my rough measurements it is apparent that the ADC design is not performing as specified in the datasheet.  I suspect this is largely due to the PCB layout.  The ADC is a mixture of very low level analog (uV levels) and 3.3V / 16Mhz digital. I see grounding rules mentioned several places in EMRFD but there was little specific guidance.  Being a digital wonk I find this particularly challenging.   Does anyone have any guidelines or commentary from experience regarding PCB layout for mixed signal designs?  Thanks Randy AD7ZU
13373	2016-12-18 10:11:49	kg4rll	Re: Grounding Rules?
Hi Randy, This may help you out, from Analog Devices. https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.analog.com/media/en/training-seminars/design-handbooks/Basic-Linear-Design/Chapter12.pdf&ved=0ahUKEwi69-2D4f3QAhWLKiYKHU4gDjAQFgg3MAE&usg=AFQjCNE5WGgu1VvShkMJiv0wWg7-8QIvEQ&sig2=LfR9zHYxvfae-NZ-j0yYDQ The information in the PDF goes into quite a bit of detail. Hope this helps, kg4rll Scott
13374	2016-12-18 10:50:29	arfghans	Re: Grounding Rules?
Does the ADC manufacturer offer an eval board? Instructions for the board often include PCB art that you can copy into your design. Didn't the datasheet include layout recommendations?  The input interface is often the culprit in compromised SFDR. Most ADCs these days have differential inputs, and if you can keep your signal differential (including the ADC drive amplifier) right up to the chip, life will be much better. Analog Devices and Linear Tech have a lot of guidance on this subject. Gary NA6O
13375	2016-12-18 11:56:13	Todd F. Carney / ...	Re: Grounding Rules?
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13376	2016-12-18 20:33:00	AD7ZU	Re: Grounding Rules?
thanks Gary, Scott, Todd, The AD paper is an excellent resource! I just read through it and have multiple changes in mind and will reread so
13381	2016-12-18 23:52:26	Todd F. Carney / ...	Re: Grounding Rules?
Here's another set of guidelines for RF grounding and PCB layout from Maxim: https://www.maximintegrated.com/en/app-notes/index.mvp/id/5100 73, Todd ------------------------------------------------------------------------------------ ​ K7TFC / Portland, Oregon, USA / ​CN85pl / UTC- ​8  (PST) ------------------------------------------------------------------------------------
13389	2016-12-19 18:09:56	kg4rll	Re: Grounding Rules?
Hi Randy, I had to read it a couple of times as well. Thanks for bringing the topic for discussion, I first read the AD document on grounding a couple of years ago and it really helped me have success with my PCB designs. Good luck with the project and let us know how it's going. kg4rll Scott